In repairing broken bones, for example a broken femur, a common approach is to insert a tubular part called a femoral nail into the interior of the bone, and then secure it in place with one or more transversely extending screws. In order to achieve this result, a screw hole must be drilled in the bone in direct alignment with each transverse hole in the femoral nail after the femoral nail has been inserted in the bone. The drill should preferably pass cleanly through the transverse hole in the femoral nail, because otherwise it will produce metal chips and shavings from the femoral nail which may impede healing and may also be a source of future discomfort or pain for the patient. However, since the femoral nail is disposed inside the bone, is not possible to directly see the hole, and thus some arrangement must be provided to accurately align a surgical drill with the transverse hole through the femoral nail.
One approach has been to use X-rays to view the hole as the drill is being aligned with the hole and during the actual drilling, but this approach exposes the surgeon and other personnel to a certain degree of radiation for a relatively long period of time in comparison to that used for a standard X-ray photograph, which obviously presents health concerns.
Another traditional approach is to provide a magnetic source outside the body and a magnetic detector within the femoral nail at the transverse hole. The detector in the nail is coupled through wires to an indicator arrangement external to the patient, and the source of magnetism is moved until the detector indicates a maximum field, at which point it is assumed that the magnetic source is aligned with the opening in the nail. However, it is difficult to precisely detect the exact maximum of the field, because the field strength is relatively uniform in the general region of the maximum. Thus a certain amount of play or slop in the position of the magnetic source can occur without any significant variation in the field strength reading on the indicator arrangement, making accurate alignment difficult. Moreover, these arrangements typically ensure that drilling starts at a point which is approximately on the axis of the transverse hole through the nail, but do not ensure that the drill is properly axially aligned with both of the diametrically opposite openings defining the transverse hole along the full length of the drill so that the drill will pass cleanly through both openings in the nail with little or no direct contact with the nail.
Accordingly, an object of the present invention is to provide an arrangement capable of providing drill alignment which is substantially more accurate than that provided by known devices.
A further object is to provide an alignment arrangement which provides precise axial alignment of the entire length of the drill along the axis of the transverse hole.
A further object is to provide such an alignment arrangement which is easy to use.